h

1. Using a unit hydrograph to
determine storm streamflow
Problem 2.2 as an example. Determine the storm hydrograph
resulting from the rainfall pattern shown, given the triangular 1-hr
unit hydrograph
Why? Unit Hydrographs are used in hydrologic design to
determine the streamflow hydrograph that would result from a given
rainfall input. When combined with design rainfall they are used to
determine design flows so that control or containment structures
(e.g. culverts, detention basins) can be properly sized.
U
(cfs)
Time (hr)
0.5
1.0
0
0 1 2 3 4 5 6
3
2
1
0
0 1 2 3 4
Time (hr)
i
N
(in/hr)

2. Synthetic Unit Hydrographs
The UH represents the integrated effect of size, slope,
shape and basin storage characteristics in converting
excess rainfall input into streamflow
Empirical equations relate UH properties to basin
characteristics
Snyders (p130-133) SCS (p133-141)

3. Problem 2.4
• A small watershed has the characteristics given
below. Find the peak discharge Qp, the basin lag
time tp, and the time base of the unit hydrograph TB
using Snyder’s method
A = 150 mi2
Ct = 1.7
L = 27 mi
Lca = 15
Cp = 0.7

4. Copyright ©2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Hydrology and Floodplain Analysis, Fourth Edition
By Philip B. Bedient, Wayne C. Huber, and Baxter E. Vieux
S-Curve Method – to construct a UH of any Duration

5. Copyright ©2008 by Pearson Education, Inc.
Upper Saddle River, New Jersey 07458
All rights reserved.
Hydrology and Floodplain Analysis, Fourth Edition
By Philip B. Bedient, Wayne C. Huber, and Baxter E. Vieux
Figure 2-9

6. Problem 2.14
• Using Excel develop the S-curve for the given 3-hr
UH and then develop the 2-hr UH from the 3-hr UH
Time (hr) U(cfs)
0 0
1 75
2 180
3 275
4 280
5 210
6 130
7 60
8 30
9 15
10 5
11 0
0
100
200
300
0 5 10 15
U(cfs)